The compound of formula (1), as the compound which has been disclosed in International Patent Publication WO 06/104356, exhibits a good inhibitory activity for Dipeptidyl Peptidase-IV enzyme, and therefore can be effectively used for treatment and prevention of diseases caused by the action of Dipeptidyl Peptidase-IV, including diabetes (particularly, type II diabetes), obesity, etc.
The methods for preparing the compound of formula (1) by means of the compound of formula (2) as the intermediate have been disclosed in WO 06/104356. Regarding said prior reference, the compounds of formulas (1) and (2) can be prepared by methods—for example, such as the following reaction scheme 1:

However, in mass-scale production said prior method is difficult to obtain the compound of formula (2) having a high optical purity due to the racemization of a stereogenic center on which the amine group is present in the compound of formula (2) to some extent, and therefore it is also difficult to obtain the compound of formula (1) with a high optical purity.